gistfile1.txt

NBTMessageHandler継承してhandle実装したクラス作ってインスタンスをNBTMessageHandler#setHandlerで設定
後はパケット投げたい所でNBT作ってNBTMessageHandler.handler使って投げるだけです

細かい部分は察して

NBTMessage.java

package net.firsp.lib.packet;

import cpw.mods.fml.common.network.simpleimpl.IMessage;
import io.netty.buffer.ByteBuf;
import net.minecraft.nbt.CompressedStreamTools;
import net.minecraft.nbt.NBTTagCompound;

import java.io.ByteArrayInputStream;

public class NBTMessage implements IMessage {


    NBTTagCompound nbt;

    public NBTMessage(String channel, NBTTagCompound nbt){
        this.nbt = new NBTTagCompound();
        nbt.setString("channel", channel);
        nbt.setTag("tag", nbt);
    }

    public NBTMessage(){

    }

    public NBTTagCompound getNBT(){
        return nbt;
    }

    @Override
    public void fromBytes(ByteBuf buf) {
        try{
            byte[] arr = new byte[buf.readInt()];
            buf.readBytes(arr);
            nbt = CompressedStreamTools.readCompressed(new ByteArrayInputStream(arr));
        }catch(Exception e){
            e.printStackTrace();
        }
    }

    @Override
    public void toBytes(ByteBuf buf) {
        try{
            byte[] arr = CompressedStreamTools.compress(nbt);
            buf.writeInt(arr.length);
            buf.writeBytes(arr);
        }catch(Exception e){
            e.printStackTrace();
        }
    }

}

NBTMessageHandler.java

package net.firsp.lib.packet;

import com.google.common.collect.Maps;
import cpw.mods.fml.common.network.NetworkRegistry;
import cpw.mods.fml.common.network.simpleimpl.IMessage;
import cpw.mods.fml.common.network.simpleimpl.IMessageHandler;
import cpw.mods.fml.common.network.simpleimpl.MessageContext;
import cpw.mods.fml.common.network.simpleimpl.SimpleNetworkWrapper;
import cpw.mods.fml.relauncher.Side;
import net.minecraft.nbt.NBTTagCompound;

import java.util.Map;

public class NBTMessageHandler implements IMessageHandler<NBTMessage, IMessage> {

    public static final SimpleNetworkWrapper handler = NetworkRegistry.INSTANCE.newSimpleChannel("NBTPacket");

    private static final Map<String,NBTMessageHandler> handlers = Maps.newHashMap();

    public static void setHandler(String channel, NBTMessageHandler handler){
        handlers.put(channel, handler);
    }

    static{
        handler.registerMessage(NBTMessageHandler.class, NBTMessage.class, 0, Side.CLIENT);
        handler.registerMessage(NBTMessageHandler.class, NBTMessage.class, 1, Side.SERVER);
    }

    @Override
    public IMessage onMessage(NBTMessage message, MessageContext ctx) {
        NBTTagCompound tag = message.getNBT();
        String channel = tag.getString("channel");
        if(handlers.containsKey(channel)){
            return handlers.get(channel).handle(tag.getCompoundTag("tag"), ctx);
        }
        return null;
    }

    public IMessage handle(NBTTagCompound tag, MessageContext ctx){
        return null;
    }
}